An Afghan girl walks amid the rubble of shops in Shadel Bazar after the US military dropped a GBU-43 Moab bomb in Achin district of Nangarhar province, Afghanistan.
Photograph: Ghulamullah Habibi/EPA

The Afghan commando knew when the big bomb would hit, so he turned on his phone camera to capture the impact.

When the blast came at 7.32pm – as the Americans had said it would – a giant white flash lit up the evening sky over the Spin Ghar mountains. But the explosion was not as loud as he had expected, the commando said. In the moment, it felt more like an earthquake.

'It felt like the heavens were falling': Afghans reel from Moab impact

The bomb was the culmination of an offensive launched in early April to push Isis back. About a kilometre from the blast site, on a hill above Shadel Bazar, which derives its name from a history as an opium market, Afghan special forces have now set up base in a shady grove named Asadkhel.

American special forces “advisers”, resting 50 metres away, ordered their Afghan colleagues – unsuccessfully – not to talk to reporters.

The commandos looked weary, but they livened up when talking about Isis. On a tour of the area, they pointed to locks of curly beard and worn-out shoes which they said belonged to dead Isis fighters.

“It gives us a lot of pleasure to kill them,” said the commando, who asked not to be named as he was not authorised to speak to the press.

For Islamuh Ahmad, an elderly resident of Shadel Bazar – about two miles from the blast site – the Moab detonation meant that he could come home.

Islamuh Ahmad, an elderly resident of Shedal, returned this week after fleeing the village over two years ago. “Isis were so cruel to us,” he said. Photograph: Sune Engel Rasmussen/The Guardian

He found the village, which normally houses up to 2,000 families, all but abandoned. A few farmers and children were walking the green fields, but Shadel Bazar was eerily quiet.

The village bears the marks of a frontline, which it was for months. A burned-out front of a car greets arrivals at the village entrance. Storefronts are boarded up with padlocks, although only a front mud wall remains.

The local school has been almost obliterated. In front of it are two unmarked graves where two Isis fighters were recently buried by villagers, supposedly to prevent their corpses from rotting in the sun.

A large private compound containing an orchard appears to have been used by Isis as sleeping quarters and training grounds. The walls are pockmarked with bullet holes and scrawled with chest-thumping graffiti: “Islamic State forever” and “Khorasan” – the name of the Afghan Isis branch. More recent ones read: “Death to Isis” and “Long live the national army”.

“When Isis blew up 10 men,” said Atebar Gul, remembering one such incident, “the people fought back. But then Isis became stronger and took revenge.”

Yet Gul was one of the few residents of Shedal who did not flee. He lived right on the frontline, but said Isis largely left him alone, perhaps because he is an old man. He also supported the American airstrike.

“Isis were dangerous for the government,” he said.

Though residents are slowly trickling back into Shedal, war is never far away. During the Guardian’s visit, two American helicopters and a fighter jet circled overhead. Every 20 minutes or so, the crack of more airstrikes punctured the silence.

The “mother of all bombs” was dropped on a complex of Isis tunnels on a mountain slope. Since the strike, US forces have conducted clearing operations. Assessing the damage is complicated by the collapse of the tunnels and risk of explosive ordnances.

Afghan authorities indicate that the Americans have allowed them limited access to the blast site, though it is unclear how much.

The same goes for the casualty toll. The Afghan government says 92 Isis militants were killed, but with restricted access to the site and bodies likely charred and buried underground, that number seems inconclusive. The US military has yet to put out an official estimate. Reports of civilian casualties are few and unconfirmed.

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The bombing raised questions about the necessity of deploying the largest weapon ever used by the US against a few hundred militants. Not only is Isis a comparably small militia in the broader Afghan insurgency, it is also geographically isolated.

While the Taliban number tens of thousands of fighters, and are amassed on the cusp of numerous provincial capitals, the bulk of Isis’ estimated 600-800 fighters are tucked away in remote mountains.

The road to the Isis stronghold in Achin runs east from the bustling provincial capital Jalalabad, then south toward the snow-capped mountains lining the Pakistani border. Thick with shrubs and trees, the area provides ample cover for insurgent fighters. Government forces control little outside the road.

As asphalt gives way to rubble, the population thins. Achin district seems almost deserted. Small groups of children herd cattle in the fields. A few men carry shovels along the road. Visible government presence is limited to a fortified administrative centre and an Afghan army base on a hill.

In Achin, Isis members have access to mines, timber, opium, an untamed border with Pakistan – and the same nearly impenetrable mountains that US warplanes have pounded since the beginning of the war.

After increasing airstrikes last year, the US managed to contain Isis to four districts in Nangarhar, and kill a number of its fighters. With the latest Moab strike, local security officials hope the group is finished.

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“Their backbone is broken. Most of their commanders are killed,” said Abdul Rahman Rahimi, the provincial police chief. “They brought their families and planned to settle but most of the families have now gone back across the Durand Line [to Pakistan].”

He said critics of the strike were foreigners or city people who didn’t understand the suffering of living under Isis.